In conventional ice cream production, liquid ice cream mix is pumped through a scraped surface heat exchanger. Vaporizing refrigerant (typically approximately −30° C.) in the jacket surrounding the heat exchanger barrel allows for energy transfer out of the mix, resulting in the formation of ice crystals. These ice crystals are scraped from the internal surface of the heat exchanger by rotating blades and collected in the center of the freezer barrel where the ice crystals grow to a mean size of 30-35 μm. The rotating blades also introduce air into the mix through whipping. Pressurized air can also be introduced into the freezer in order to aid in whipping. These freezers can be constructed as batch or continuous operations and the ice cream is usually drawn from the freezer in a partially frozen state so that it is still flowable. Many variations of these types of systems are available commercially.
Regardless of the system, several parameters are critical to the end quality of the ice cream including ice crystal formation, air incorporation, air cell formation, and fat globule destabilization. Ice crystal formation is heavily influenced by the freezing process. In order to keep ice crystals in the desirable range for optimal eating quality, freezing must promote the formation of ice crystal nuclei, but limit crystal growth. Practically, high nucleation rates can be achieved by rapid freezing with low temperature refrigeration (≤−30° C.). Minimizing crystal growth is more complicated and less well understood, but minimizing residence time in the freezer barrel is one accepted approach.
The present invention is directed to overcoming these and other deficiencies in the art.